Automatically operating control arrangement for pairs of rollers



Jan. 28, 1958 INVENTOR Hmvs DON/7TH ATTORNEY United States Patent '0AUTOMATICALLY OPERATING CONTROL ARRANGEMENT FOR PAIRS OF ROLLERS HansDonath, Dresden, Germany, assignor to VEB Muhlenbau, Dresden, GermanyApplication October 19,1954, Serial No. 463,261

5 Claims. (Cl. 241--35) This invention-relates to driving means forroller mills,

and particularly to a freely acting differential gear for driving pairsof rollers in such mills and to a control arrangement for automaticallyregulating the roller speed.

As is generally known, pairs of rollers have been used for a long timein industry for a great variety of purposes. The pairs of rollersemployed in roller mills are mounted in frames and have a grinding orpulverizing action on the material by being driven in oppositedirections at different peripheral speeds. Pairs of rollers of this typeare used in the milling industry, but also for grinding and pulverizingother materials, as wood, minerals or the like.

The invention refers to a roller mill particularly intended for grindinggrain, and is particularly directed to a regulating device whichautomatically controls the speed of the rollers in dependence upon theturning moment ratio in the differential gear.

Banks of rollers were adjusted hitherto according to the experience andtouch of an operator, i. e. by variable factors which could not bepredetermined, and accordingly different results in regard to thequality of the product were obtained. This method was noteconomical, andtests have therefore been made to ascertain the variables involved inorder to establish results which could be repeated. As a result of thesetests roller mills have been developed, in which the control andregulation is effected by special devices. For instance, in order toobtain the differential velocities, infinitely variable speedtransmissions have been used, in which either one roller or both havebeen regulated by a continuously variable speed control. In these casesthe difference in speed, that is to say the ratio of revolution of thetwo rollers, was maintained constant at a certain value determined bycalculation. The resultant effect is, however, not wholly dependent onrelative speeds and absolute speeds, but

also on the adjustment of the gap between the rollers.

This adjustment also requires great experience and is effected by knownapparatus according to tests. All known devices have been provided withmeasuring indicators, so that the parts could be adjusted according tofactors obtained by tests or from experience to get the best grindingaction with the least expenditure of power.

All these methods and devices have been found, however, to becomplicated and difficult to watch, so that in practice they have notbeen generally adopted. In view of the necessity of constantreadjustment, they required careful inspection in order to obtain thedesired effect.

The invention eliminates these disadvantages and provides a roller mill,in which variations in power output are automatically regulated by thebalancing of the power output of the slow and fast rollers. For thefirst time a completely automatic roller bank is constructed which isautomatically put out of or into action only when the material to beground is changed or the gap between the rollers has not been setproperly. The adjustment of the gap is hereby facilitated and need onlybe effected once. In this may, a uniform, excellent quality of materialwith highest throughput and least power consumption is obtained.

According to the invention, the roller mill is provided with a freelyacting differential gear driving both rollers and comprising anepicyclic train which by way of a set of planetary wheels operates asdifferential gear and the construction of which is such that a reverselyrunning element of the gear rotates at a speed equal to the sum of thespeeds of rotation of the rollers. Owing to this arrangement, thedifference in speed of the two rollers can be varied with certainlimits, and the dimensioning of the elements of the gear determines therelative turning moments acting therein. Due to the provision of adifferential gear and by the action of the planetary wheels, acompletely automatic method of operation is obtained, as the adjustmentand correct running of the pair of rollers is considerably facilitated.By this means the risk of over or dead-milling is avoided and thedisplacement of passages considerably reduced. Further, it is possiblewith a differential gear to control the output automatically without theinterposition of a regulating drive, for instance by directly drivingthe feed rollers from the slow running roller.

It is also now possible, by adjusting the free element of the drive, toobtain a corresponding reversal of the method of operation. By using adifferential gear having a reversely running planetary wheel allrequirements can be met for an automatic control of the pairs of rollerswith a single or double stage planetary wheel arrangement. By this meansa constant turning moment can be obtained.

The known automatic roller mills include only an automatic feed for thematerial to be ground, which prevent a reversal of movement of thematerial in the process and require an automatic closing up or movementapart of the rollers. This is very diflicult to effect, and differencesof output result from the constant gap between the rollers, which givesdifferences in grinding effect. Operation according to the invention istherefore wholly automatic.

In order to simplify the apparatus, a differential drive to two or moregrinding shafts can be established, so that the rollers operate with thesame turning moment, either being driven directly or in a step-downratio.

The small space required for the differential gear allows it to bemounted within the rollers, so that increased milling capacity isobtained in the same space as hitherto.

By this invention, due to the increased speed of transmission of thedriving and transmission elements, considerable material is saved inconstruction, and it is no longer necessary to use servo-motors, controlelements or continuously variable speed drives. The invention provides aquiet drive which can be maintained for long periods with efficiency, asthe differential drive can be wholly enclosed in an oil bath.

The arrangement of the invention is further described with reference tothe accompanying drawings. In these, application of the invention isshown to a bank of rollers as used for grinding flour or like purposes.It is obvious that the invention can be applied to special requirementsin other forms of banks of rollers by maintaining the principle of theinvention. To explain the invention fully, the requirements for a milldrive are set forth in detail below. In the drawings Figure 1 shows, byway of example, an arrangement of a differential gear driving a pair ofrollers; and

Fig. 2 is a diagrammatic view of a roller bank particularly suitable forgrinding flour.

In known manner, the two rollers 1 and 2 of a bank of rollers aredisposed on parallel axes in bearings 3, so that in order to alter thegap 4 between the rollers, one roller is adjustable radially of theother. The rollers rotate with differing peripheral speeds, and theroller 1 acts as a high speed cutting r ouer" while the slower roller 2feeds and grips the grain.

The roller 1 carries on its driving shaft a difierential gear. This canbe of any desired-form, and any differential gear can be used where thetorque applied to the driving shaft is normally transmitted to the twodriven rollers in a predetermined ratio, regardless of the respectivepower outputs.

In the arrangement shown, the differential gear consists of a beltpulley 5 to which the drive is taken and which is fixed to a casing 7having an internal ring gear 6. A sun wheel 9 is keyed on the shaft 8 ofthe fast roller 1, and simultaneously serves as a bearing for the pulley5. A carrier 10 is mounted for rotation in the casing 7 about the stubshaft 8 and carries planet wheels 11 meshing simultaneously with the sunwheel 9 and the ring gear 6. The cylindrical boss of the carrier 10mounted on the shaft 8 also serves as a bearing for the casing 7 towhich the pulley 5 is fixed. The boss further carries a sprocket wheel12 which is directly connected with the shaft 13 of the roller 2, forinstance by a chain drive 14. The drive for the slow roller 2 is therebystepped down. A belt pulley is keyed to one end of the slow roller 2,which drives by means of a belt 22 the feed rollers 16 and 17 arrangedabove the rollers 1 and 2. Adjustable feedplates 18 of known type andconstruction are disposed above the two feed rollers to control the flowof material to said feed rollers 16 and 17. Should the grindingoperation or the flow of material to be ground vary during operation ofthe machine, this will have an immediate effect on the relative speed ofrotation of the two rollers 2 and 1 by reason of the dilferential gear.By the driving of the feed rollers 16 and 17 directly from the roller 2,the necessary change is effected in the speed of the feed rollers.

By this means the flow of material to be ground is varied until theturning moment has again become equal.

I claim:

1. An automatic speed control for a roller mill comprising incombination: a first rotatable roller, a second rotatable roller, aditferential gear including a driving element and two driven elementsoperatively connected with each other, and a speed reductiontransmission, one of said driven elements being operatively connectedwith said first roller, the other driven element being operativelyconnected with the input end of said speed reduction transmission, andthe outputend of said speed reduction transmission being operativelyconnected with said second roller.

2. In an automatic speed control for a roller mill, as claimed in claim1, at least one rotatable feed roller, and driving means operativelyconnecting said second roller with said feed roller for rotating thelatter in dependence on the rotation of said second roller.

3. An automatic speed control for a roller mill, comprising incombination: a first rotatable shaft, a first roller rigid with saidfirst shaft, a second rotatable shaft, a second roller rigid with saidsecond shaft, a carrier rotatably mounted on said first shaft, aplurality of planet gears rotatably'inounted on said carrier, a sunwheel keyed to said first shaft, a driving housing having an internalgear, said housing rotatably mounted on said carrier, said planet gearsbeing in mesh with said sun wheel and said internal gear, and atransmission operatively connecting said carrier-with said second shaftfor rotating the latter in dependence on a rotation of said carrier.

4. In an automatic speed control for a roller mill as claimed in claim3, said transmission being in the shape of a speed reductiontransmission for driving said second shaft at a speed lower than that ofsaid first shaft.

5. In an automatic speed control for a roller mill as claimed in claim3, at least one rotatable feed roller, and driving means operativelyconnecting said second shaft with said feed roller for rotating thelatter in dependence on the rotation of said second shaft.

References Cited in the file of this patent UNITED STATES PATENTS392,782 Clamsen et al. Nov. 13, 1880 1,880,690 Berry Oct. 4, 19322,531,032 Desinoulines Nov. 21, 1950

